On Sep 13, 7:48*pm, Orval Fairbairn
wrote:
In article ,
*Robert Moore wrote:



Orval Fairbairn wrote
In the case of the firefighting plane, if it was flying level and
dropped a large weight (slurry), the wings would have the same load,
either with or without the dropped weight. Other airframe components,
such as engine mounts, fixed equipment, crew, however, would
experience a sudden increase in G loading. If the plane was flying at
too high speed, sudden updrafts/gusts could overload the wings.

Say What!!

You may know what you are trying to say, but it sure didn't come out
making sense.

From Wikipedia:
The g-force experienced by an object is its acceleration relative to
free-fall. The term g-force is considered a misnomer, as g-force is not
a force but an acceleration.

You probably meant to say "wings would have the same LOAD FACTOR".
Clearly, the load supported by the wing of a loaded aircraft is more
than the wing loading of an empty aircraft even though both are
experiencing only 1g. If the pilot doesn't reduce the angle of attack
(amount of lift produced by the wing)as the load is dropped, the wing
root will experience an increase in g-force. G-force is equal to the
actual lift being produced by the wing (at that angle of attack and
airspeed) divided by the weight being lifted.

From a aerodynamic viewpoint, the smart thing to do would be to push-
over (reduce the angle of attack) just as the fire retardant is
released, thereby reducing the g-force on the wing root. This, however,
tends to prevent the retardant from exiting the aircraft. What the
pilots seem to be doing is pulling up AND turning at the point of drop
and thereby making a bad situation even worse.

Bob Moore

It is a paradox here.

Structurally, a wing really doesn't care WHAT the G-force is! All the
structure is concerned about is the amount of stress on its components.
A wing carrying, say 200K#, which suddenly drops 100K# will pull 2G, but
the STRESS on the wings remains 200K#. Other components of the aircraft
will experience 2G, but the wing's stresses remain the same.

--
Remove _'s *from email address to talk to me.

Wouldn't there also be a torsion moment caused by the pitch up, i.e.,
the configuration of trim for level flight would create a nose/pitch
up after release, increasing AOA rapidly and 'twisting' the wings off
at the roots? The wings would actually be trying to increase AOA
ahead of the more massive fuselage.

Or, if not torsion then indeed it was more like an updraft in that the
rapid pitchup increased the AOA at such a rate as to literally 'blow'
the wings off. Picture it as an effect similar to holding your hand
outside the car window then quickly rotating it for a positive AOA.
It can quickly get away from you and give you a wrenched shoulder...
Don't mind me, I'm just thinking out loud

Here's a good article:
http://findarticles.com/p/articles/m.../?tag=untagged